The present invention relates to a signal transmitting and receiving apparatus, and more particularly to a signal transmitting and receiving apparatus suitable for transmission and reception of signals between control units or between a control unit and an I/O device of a computer.
In many process controls including conveyer control, machine tool control, waterworks/drainage system control and chemical plant control, the controls are becoming more and more complex so that reliability in a high speed process has been required and a digital computer control has been widely used.
Frequently, a control unit is coupled to a mini-computer through a bilateral bus line to control the process by the mini-computer and signals are exchanged between the control unit and the mini-computer. In such a case, parallel-by-word data received from the bilateral data bus is converted to serial-by-word data to transmit it to a peripheral device, and serial-by-word data from the peripheral device is converted to parallel-by-word data to transmit it to the mini-computer. The transmission of serial data to the peripheral device is more effective than the transmission of parallel data in reducing the number of transmission lines included.
The present invention relates to a signal transmitting and receiving apparatus suitable for such signal transmission.
2. Description of the Prior Art
Heretofore, such a signal transmitting and receiving apparatus is formed by wired logics of integrated circuits. In such a case, even an average scale circuit needs fifty to sixty integrated circuits. This has been a problem in reducing an overall size. In addition, an essential problem has existed in that a configuration of the signal transmitting and receiving circuit must be altered depending on a particular type of device to be coupled and the wired logic system cannot cover a wide range of alternation.
In a known technology to solve these problems, there has been proposed a combination of a micro-computer and a peripheral large scale integrated circuit (LSI), which is disclosed in U.S. Pat. No. 3,975,712 entitled "Asynchronous Communication Interface Adaptor" (ACIA), issued Aug. 17, 1976. The ACIA is connected to a micro-computer through a bus line. In the above-mentioned U.S. Patent, it is connected to a modem through a line 109 as shown in FIG. 2 thereof. The ACIA includes means for converting parallel data to serial data and transmitting it, means for receiving serial data and converting it to parallel data and interface buffer means for controlling the transmission and reception. However, a signal bit format is an 8-bit fixed format and there is no teaching about a control unit to be connected to the ACIA. In actual control, the bit configuration is not fixed to the 8-bit format and the control unit may be connected in various ways. However, the ACIA is not adaptable to those modifications and hence it is not universal. In addition, one of the biggest limitations is that the ACIA can be used only when it is coupled to an MPU (microprocessing unit) through a bus line. In many actual applications, however, the system does not necessarily include the microprocessor and the signals are exchanged within the system. In this respect, the use of the ACIA is limited to a case where it is coupled to a CPU.